<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue.js 监听属性</title>
    <script src="https://lf26-cdn-tos.bytecdntp.com/cdn/expire-1-M/vue/2.6.14/vue.min.js"></script>
</head>
<body>
<div id="computed_props">
    千米：<input type="text" v-model="kilometers">
    米：<input type="text" v-model="meters">
</div>
<p id="info"></p>
<script type="text/javascript">
    var vm = new Vue({
        el:'#computed_props',
        data:{
            kilometers:0,
            meters:0
        },
        method:{

        },
        computed: {

        },
        watch:{
            kilometers: function (val) {
                this.kilometers = val;
                this.meters = this.kilometers * 1000
            },
            meters: function (val) {
                this.kilometers = val/ 1000;
                this.meters = val;
            }
        }
    });
    // $watch 是一个实例方法
    vm.$watch('kilometers', function (val) {
        // 这个回调将在 vm.kilometers 改变后调用
        document.getElementById ("info").innerHTML = "修改前值为: " + oldValue + "，修改后值为: " + newValue;
    });
</script>
</body>
</html>
